Surface confined electrochemical compound formation: Incipient sulfidation of Au(1 1 1)

Abstract

The incipient electrochemical interaction between sulfur and a Au(1 1 1) surface is investigated by keeping the sulfur coverage constant. To this end the $\left( {\sqrt {3 \times \sqrt 3 } } \right)R30^\circ$ phase of sulfur on Au(1 1 1), Θ _S = 0.33 ML, is subjected to potential increases in a S-free NaOH solution. At anodic potentials the reversible formation of a rhombic phase is observed. The local S coverage increase which is required for the formation of the rhombic phase results from a coverage decrease within the $\left( {\sqrt {3 \times \sqrt 3 } } \right)R30^\circ$ regions, where single-S-atom-defects and, in later stages, S vacancy islands are formed. Furthermore, the growth of the rhombic phase is accompanied by a Au mass transport which clearly calls for a reinterpretation of its chemical nature.